The aim/s of this application are to examine the sensitivity of opiate receptors on the nucleus locus coeruleus during aging. Sensitivity of receptors will be examined after acute and chronic administration of opiates and enkephalins. This project seeks to characterize receptor sensitivity in rats by the use of electrophysiological techniques. Single identified neurons in the nucleus locus coeruleus will be studied. The effects of drugs on these neurons will be examined after systemic and iontophoretic administration. Changes in the effects of opiates and enkephalins after chronic administration will also be examined. This study should reveal whether the properties of central opiate receptors alter during aging.